Radio frequency identification (RFID) technology may be deployed in a variety of environments, including retail stores, warehouses and the like, to track various types of objects. A typical RFID system includes an RFID reader or interrogator, and a plurality of RFID tags. The tags are typically associated with objects (e.g. items of clothing, boxes of inventory or the like) within the environment, and may be physically attached to such items. The RFID reader is configured to emit a sequence of radio frequency (RF) interrogation signals, in different predefined directions. The direction of each interrogation signal is controlled by the RFID reader via the application of complex weights to each of a phased array of antenna elements, rather than via physical movement of the antenna elements.
At least one of the tags, upon receiving an interrogation signal, is configured to emit an RF response. The RFID reader, in turn, is configured to detect and demodulate the response, which may contain, for example, a stock keeping unit (SKU) code or other data identifying the object to which the tag is attached. In addition to demodulating the identifying data, the RFID reader may also be configured to estimate a bearing (e.g. elevation and azimuth relative to the RFID reader) of the tag from which the response was received, for location tracking of objects within the environment. The RFID reader may implement conventional digital beamforming techniques for bearing estimation; however, such bearing estimation techniques may still require two or more interrogations of each tag in the environment in order to arrive at a sufficiently accurate bearing estimation. The need for repeated tag interrogations slows location tracking, reducing the effectiveness of the system.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.